An OLED display device is a new-generation display device. An organic thin film, which is packaged between a cathode metal and an anode metal, is formed on an OLED substrate. When a voltage is applied to the two electrodes, the organic thin film emits light. The OLED display device has many advantages, including its capability of realizing flexible display. For example, a flexible OLED panel can be formed by using a flexible plastic substrate as a carrier and using a thin film packaging procedure.
Currently, an OLED thin film packaging structure is mainly formed by laminating a barrier layer and a buffer layer. As shown in FIG. 1 (a three-layer structure), the structure includes an OLED 2 disposed on a TFT substrate 1, a barrier layer 3 covering the OLED 2, a buffer layer 4 covering the barrier layer 3, and an outermost barrier layer 5 covering the buffer layer.
The barrier layer is made of an inorganic material such as a silicon nitride material. The buffer layer is usually made of an organic or a partially organic material. The barrier layer is used for blocking water and oxygen. The buffer layer is mainly used for eliminating strain between the two barrier layers and covering defects and pinholes in the barrier layers. The barrier layer and the buffer layers can both be prepared by a plasma-enhanced chemical vapor deposition (PECVD) machine.
The PECVD machine needs to be provided with a mask. The mask covers an OLED device on which a thin film is formed by a gas flowing through an opening of the mask. The OLED device is thus isolated from outside air, and thin film packaging is realized.
In order to avoid invasion by water and oxygen from a side of the OLED device, an area of an outer thin film is required to be larger than that of an inner one, ensuring that sides and a top of the OLED device are protected by a same quantity of thin films. FIG. 2 (a), FIG. 2 (b), FIG. 2 (c), FIG. 2 (d), and FIG. 2 (e) show five steps of an OLED thin film packaging method, in which barrier layers and buffer layers are sequentially provided on the OLED device. In FIG. 2 (a), a barrier layer is coated on the OLED device; in FIG. 2 (b), a barrier layer is coated on the buffer layer in FIG. 2 (a); and these operations are repeated in following steps. This requires that an opening of a mask used for depositing an outer thin film be larger than that of a mask used for depositing an inner thin film. For a structure consisting of, for example, five thin films, five different masks are required. When two kinds of thin films are prepared in a single cavity, masks need to be changed for four times (a first mask is already in the machine). Because currently, the PECVD can prepare both the barrier layer and the buffer layer, out of consideration of costs, in research, many institutes use only a single cavity to prepare two kinds of thin films. This can leads to inter-pollution between the two kinds of thin films. Furthermore, masks need to be frequently changed (a mask needs to be changed once a thin film is formed). Frequent changing of masks produces a large number of particles, which are considered as one of the main factors affecting a packaging effect of the thin film. Water and oxygen may enter into the packaging structure through gaps at edges of the particles. For a thin film packaging structure, it is therefore significant to reduce the quantity of the particles.